Science & Environment

Science chief warns on acid oceans

Corals
Image caption Some corals are unlikely to last out the century

The UK's chief scientist says the oceans face a serious and growing risk from man-made carbon emissions.

The oceans absorb about a third of the CO2 that’s being produced by industrial society, and this is changing the chemistry of seawater.

Sir Mark Walport warns that the acidity of the oceans has increased by about 25% since the industrial revolution, mainly thanks to manmade emissions.

CO2 reacts with the sea water to form carbonic acid.

He told BBC News: “If we carry on emitting CO2 at the same rate, ocean acidification will create substantial risks to complex marine food webs and ecosystems.”

He said the current rate of acidification is believed to be unprecedented within the last 65 million years – and may threaten fisheries in future.

The consequences of acidification are likely to be made worse by the warming of the ocean expected with climate change, a process which is also driven by CO2.

Sir Mark’s comments come as recent British research suggests the effects of acidification may be even more pervasive than previously estimated.

Until now studies have identified species with calcium-based shells as most in danger from changing chemistry.

But researchers in Exeter have found that other creatures will also be affected because as acidity increases it creates conditions for animals to take up more coastal pollutants like copper.

Shock result

The angler’s favourite bait – the humble lugworm – suffers DNA damage as a result of the extra copper. The pollutant harms their sperm, and their offspring don’t develop properly.

“It’s a bit of a shock, frankly,” said biologist Ceri Lewis from Exeter University, one of the report’s authors. “It means the effects of ocean acidification may be even more serious than we previously thought. We need to look with new eyes at things which we thought were not vulnerable.”

The lugworm study was published in Environmental Science and Technology. Another study from Dr Lewis not yet peer-reviewed suggests that sea urchins are also harmed by uptake of copper. This adds to the damage they will suffer from increasing acidity as it takes them more and more energy to calcify their shells and spines.

This is significant because sea urchins, which can live up to 100 years, are a keystone species - grazing algae off rocks that would otherwise be covered in green slime.

Image caption Ceri Lewis from Exeter University studies the effects of acidification on marine life

Dr Lewis found that at the pH expected by the end of the century, sea urchins will face damage from copper to 10% of their DNA.

Urchins are in an unfortunate group of creatures that look most likely to suffer from changing ocean chemistry.

At the bottom end of the marine animal chain, tiny creatures like plankton and coccolithophores reproduce so fast that their future offspring are likely to evolve to cope with lower pH.

At the other end of the scale are fish and crustaceans which are able to control their internal chemistry (even though some fish are affected in unexpected ways by acidification).

But the long-lived urchins are too simple to control their own body chemistry and will find it harder to adapt. They’re likely to be in trouble, along with molluscs like mussels - which provide food for predators and also perform vital services to the eco-system.

Tough, boulder corals may survive the changes, but many of the branching and table corals which provide shelter for tropical fisheries are judged unlikely to last out the century.

Slow recovery

The recent meeting of the UN’s convention on biodiversity warned that it can take many thousands of years for marine life to recover from acidification.

Dr Lewis said that it was straightforward to forecast future chemical changes to the ocean. She said predictions of future pH had drawn few of the criticisms levelled at the much more complex models of climate change.

But she warns that the biological effects of the chemical change in the oceans are harder to predict.

In her Exeter lab she is currently subjecting ill-tempered crabs to the end-of-century challenge. She plunges her hand into a seawater tank to seize the shell of one feisty specimen that does not want to be moved. It grips the water feedpipe with a vicious-looking claw.

“We think crabs should fare better with low pH than urchins do,” she tells me.

“We don't know yet how they will respond to extra availability of copper.

“Our work means we are under-estimating effects of acidification for coastal invertebrates. We are now realizing there are many indirect impacts of ocean acidification on other processes. It could be that we are facing a lot more surprises ahead.”

Dr Lewis has set herself a mission to explain the science of ocean acidification to children. Along with other ocean experts she wrote to the government urging the education department to guarantee a place for the oceans in the school science.

“It’s unacceptable that pupils can go through their entire school science career learning nothing about the oceans which cover 70% of the planet,” she says. “Ocean acidification is a fact – children should know that.”

Follow Roger on Twitter @rharrabin

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